Dothistroma needle blight is an economically important tree disease caused by two fungal pathogens, Dothistroma septosporum and Dothistroma pini. Although the disease has been a problem in the southern hemisphere for many years, only recently has it caused significant damage to plantations and natural forest ecosystems in Europe. The biosecurity implications relating to this recent upsurge are unclear, and this has raised a number of important questions: Are these fungi recently introduced, or is it that they are changing in behaviour, possibly due to changing climatic conditions? Alternatively, is the dramatic increase in disease intensity and geographical and host range due to the introduction of more aggressive strains? Is this situation likely to worsen, or maybe improve under future management and climate change scenarios? What are the most suitable management strategies? This Action, DIAROD, plans to build on the foundations of the International Dothistroma Alliance (IDA), established in 2006 to help combat the new problems faced due to this disease. The aim of the DIAROD cost Action is to synthesize knowledge, encourage collaborative research to address the key questions, determine future research priorities, and use the resulting information to develop management strategies applicable to this evolving disease and other future disease threats. The COST Action is organised into four working groups: Determining Invasiveness And Risk Of Dothistroma (DIAROD); The pathogen - defining the current disease situation; The environment: determining the risk of DNB; The host - resistance and susceptibility; Identifying research gaps and dissemination. It will run from 2011 to 2015.